LKK wrote:I installed a Tesla Powerwall 2 with a SolarEdge system. The system works well. During the day excess solar power is first used to charge the battery and when it is fully charged the power is sent to the grid using a net metering power purchase agreement. When the sun goes down the power is first drawn from the battery via an integrated 5 kw inverter and when it is depleted, power is drawn from the grid.
If the grid fails the Powerwall isolates itself from the grid and uses its integrated inverter to supply a 240 VAC signal to the SolarEdge net tied inverter to allow it to function in backup mode. There are two subpanels in my system, one for backed up circuits the other for unbacked circuits. The criteria used to decide if a circuit is backed or not is the power capacity of the integrated inverter. It will handle 7 is peak and 5 is continuous, you have to decide which circuits you want backed based on their power consumption and the capacity of the battery. The subpanels are next to each other so it is relatively easy to move a circuit from one subpanel to the other. In my system I backed all the 120 VAC circuits and put all the heavy load 240 VAC circuits in the unbacked side. I should add when the system is operating normally the battery supplies power for both subpanels when solar power is not available.
The battery capacity is around 13.6 kwh. You can set the amount of usable capacity in the Tesla app. The battery is liquid cooled. The Tesla app has been very useful showing power flows between the solar, battery, home and grid in instantaneous and accumulated power over different periods.
The main advantage of the battery for me is rate arbitration. With solar I'm forced on to a time-of-use rate schedule where the main daylight hours are classed at off peak and late afternoon and evening hours are the peak period. Off peak is around $.25/KWH, peak is double that at $.50/KWH. So instead of sending excess solar power to the grid, it makes much more sense to store this power in a battery that becomes active during peak hours. This could save up to $7/day on a 14 KWH battery. The new net metering rates being forced on new solar users without this battery, is in my opinion totally useless.
Here in California a Self Storage rebate is being offered which significantly offsets the cost of the battery.
I was lucky, i installed my solar array when they did like for like net metering.. so anything I put in I get back at the same rate. They could change that I think, at anytime to suit them. so this setup is the best, the one you have. I'd do it. But since our power company has a flat rate all day each day.. not much of an incentive to do such a system yet. I'll have to watch closely to see what happens. right now the grid is my battery but they've been harping on about it some recent mailings to the city, which pretty much calls residents with solar 'thieves', though they don't go as far but it's implied.